Investigation 12. The Hand Warmer Design Challenge: Where does the Heat come from?

Transcription

1 Investigation 12 The Hand Warmer Design Challenge: Where does the Heat come from?

2 Safety Solids are eye and skin irritants. CaCl 2 can cause skin burns. Wear googles at all times. Failure to do so will result in a 0 for the lab. No warnings. I see you with your goggles off you fail the lab. If solutions are spilled on skin wash with lots of water. Dilute solutions and pour down the drain.

3 You will be assigned set of solids that you will test as it follows. Group 1- NaCl, Na 2 CO 3, CaCl 2 Group 2-NaCl, LiCl and NaC 2 H 3 O 2 Group 3-NaCl, LiCl, NaC 2 H 3 O 2 Group 4- NaCl, Na 2 CO 3, CaCl2 Group 5-NaCl, NaC 2 H 3 O 2, LiCl Review MSDS data for your solids from the website I will post on my website.

4 From the simulation remember Energy must be added to separate cations and anions in solid Energy is released during formation of the water-ion hydration spheres Magnitude of the change for these energy changes depends on the identity of the anions and cations.

5 Prelab question 1: describe changes Na and Cl ions separated from one another. Water molecules are surrounding the cations and anions and water molecules are separating from one another. Bonds between anions and cations are broken and H-bonds between water molecules are broken so now new bonds between water molecules and cations and water molecules and anions are formed. Solution is far less ordered so entropy is

6 Prelab #2- Temperature Heat is (absorbed/released) during process Amount of energy required to separate sodium and chloride ions in the crystal lattice and water molecules from one another is greater than the amount of energy released when the ion-water attraction (hydration spheres) form in resulting solution. The difference between these two amounts of energy is absorbed as heat, resulting in temperature (increase/decrease)

7 Prelab#3: Spontaneity Increase in disorder or entropy is thermodynamically favorable and this increase in entropy causes dissolution to occur spontaneously even though it is endothermic.

8 Prelab #4: temp increase or decrease? Temperature increase or decrease is determined by relative amounts of energy required to separate ions in the crystal lattice (solid) and released upon formation of water-ion attraction. If the energy required to separate ions in solid is greater then heat will be absorbed during formation of solution and the temperature of the resulting solution will be lower. If the energy that is released by the formation of ion water interactions is greater then heat released during formation of solution and solution temp will be higher than starting temp.

9 In this lab you will find ΔH sol Units are kj/mol part 1 calorimetry practice part 2 calorimeter calibration procedure.

10 Homework for tomorrow. Summarize in a paragraph what is happening in a solution regarding bonds heat exchange- Review MSDS data, making notes about safety. Design a procedure for the lab. Rank your solids from least to most expensive Helpful hints: Keep detailed records of amounts used and starting and ending temperature You only get to use 10 g of each solid.

11 DAY 2 Lab Lab procedure must be approved by me before you continue. Be mindful of the safety procedures. Answer question 1 for tomorrow. Set up investigation calculation data table as follows Useful tip: dissolve equal amount of each assigned solid in given amount of water with approximate mass of solution of 50g in each trial. For example (45.0mL water and 5.0g solid)

12 Calorimeter Constant Calculation= calorimeter constant between 10 J/C to 25J/C are reasonable.

13 Trend in your data????

14 Sample data Solid Initial Temp in C Final Temp in C Sodium acetate Calcium chloride Sodium carbonate Sodium chloride Lithium chloride

15 Solid Your Data Chart should be set up like Temp change Thermal energy in calorimeter contents q rxn (J) Thermal energy change of calorimeter q cal (J) this Internal energy change q soln (J) Molar mass (g/mol) Moles used (mol) Enthalpy of dissolution ΔH soln (kj/mol)

16 Homework for tomorrow Wednesday 12/11 Bozeman video on London forces Question #1 from data collection and computation